Fluid pressure operated motors

ABSTRACT

This invention relates to fluid pressure operated motors and in particular to such motors of the type in which a piston is mounted to exhibit axial movement in a piston cylinder and in which movement of the piston is controlled by the exhaust of liquid pressure or gas pressure from a chamber associated therewith.

United States Patent Inventor Philip Butterwortb Brarnhall, EnglandAppl. No. 794,745 Filed Jan. 28, 1969 Patented July 20, 1971 AssigneeButterworth Hydraulic Developments Limited Priority Feb. 12, 1968 GreatBritain /68 FLUID PRESSURE OPERATED MOTORS 15 Claims, 5 Drawing Figs.

US. Cl 91/239, 91/240, 91/243, 9l/263, 91/309, 91/408 Int. Cl F01I25/06Field olSearch... 91/357,

[56] References Cited UNITED STATES PATENTS 1,484,030 2/1924 Kitchen91/357 i,84l,629 1/1932 Pigealet 91/357 2,325,138 7/1943 Kyle m1 91/278FOREIGN PATENTS 374,080 5/1932 Great Britain 91/278 PrimaryExaminer-Paul E. Maslousky Attorney/Stevens, Davis, Miller and MosherABSTRACT: This invention relates to fluid pressure operated motors andin particular to such motors of the type in which a piston is mounted toexhibit axial movement in a piston cylinder and in which movement of thepiston is controlled by the exhaust of liquid pressure or gas pressurefrom a chamber associated therewith.

PATENTEU JUL20 I971 SHEET 1 OF 5 PATENTEUJULZOIBYI 3. 593-517 SHEET 2 UF5 PATENTEU JUL2O I97! SHEET 3 BF 5 PATENTED JUL 2 0 I97! SHEET 5 BF 5lFLUlllD PRESSURE ()lPEliUt'lllElD MOTORS A fluid pressure operatedmotor which includes a piston slidably mounted for axial movement in apiston cylinder and in which axial movement of the piston is adapted tobe permitted by the exhaust of fluid from a pressure chamber associatedtherewith which is caused to contract in volume dur ing axial movementof the piston; wherein the pressure chamber communicates with a controlport in the piston cylinder through which control port fluid from thecontracting pressure chamber can exhaust, said control port beingcontrolled by a land of the piston whereby, during axial movement of thepiston in a sense to contract the pressure chamber, fluid from thecontracting pressure chamber exhausts through the control port untilsaid port is closed by the land of the piston to form a blockage toexhaust of fluid from the pressure chamber and to arrest the piston atthe end of its stroke.

Preferably a plurality of ports are provided in the piston cylinderwhich are arranged in an axially disposed array and port selection meansis provided by which one or more of the ports can be selected as thecontrol port to communicate with exhaust. The array of ports arecontrolled by the piston land so that the end of stroke of the piston isdetermined when the selected port or ports are closed by the pistonland. By selecting one or more of the axially disposed ports, theeffective position of the control port in the piston cylinder can beaxially varied and hence the position at which movement of the piston isarrested by the closure of the control port or ports and consequentformation of the blockage is also varied (Le. a the end of the pistonstroke can be adjusted).

in a preferred form of construction of the motor the piston is adaptedto exhibit reciprocal movement in its cylinder and two pressure chambersare provided. One pressure chamber is adapted to alternately contractand expand and the other pressure chamber is adapted simultaneously toalternately expand and contract respectively during reciprocation of thepiston. Piston land means on the piston is adapted to control theopening and closing of two axially spaced control ports in the thepiston cylinder. A first pressure chamber, during its contraction bymovement of the piston in one sense of axial direction, is adapted toexhaust through a first control port controlled by the piston land meansand the end of stroke of the piston in the one sense of axial directionis determined by the first control port being closed by the piston landmeans. The second pressure chamber, during its contraction by move mentof the piston in the opposite sense of axial direction is adapted toexhaust through the second control port controlled by the piston landmeans and the end of stroke of the the piston in the opposite sense ofaxial direction is determined by the second control port being closed bythe piston land means. By such a construction the piston is arrested ateach end of its stroke as the control port through which the contractingpressure chamber exhausts is closed by the piston land means.Conveniently the piston has two axially spaced lands which, togetherwith the piston cylinder, define an exhaust chamber which is adapted tocommunicate with the contracting pressure chamber during axial movementof the piston. Preferably the contracting pressure chamber is adapted tocommunicate wit the exhaust chamber by way of an input port in thepiston cylinder which is in permanent communication with the exhaustchamber and is located axially between the two control ports. The firstof the control ports is controlled by a first piston land so that it isalternately opened and closed to communication with the exhaust chamberand the second of the control ports is controlled by the second pistonland so that it is alternately opened and closed to communication withthe exhaust chamber. The control ports and piston lands are ar' rangedso that at least one or other of the control ports is always open tocommunication with the exhaust chamber during reciprocation of thepiston. The first pressure chamber when contracting is adapted toexhaust by way of the exhaust chamber and the first control port so thatthe end of stroke of the piston in the first sense of axial direction isdetermined when the first control port is closed by the first pistonland. The second pressure chamber, when contracting is adapted toexhaust by way of the exhaust chamber and the second control port sothat the end of stroke of the piston in the opposite sense of axialdirection is determined when the second control port is closed by thesecond piston land. Valve means is provided which, in a first operativecondition consistent with the piston moving in the one sense of axialdirection closes communication between the second control port andexhaust and opens communication between the first control port andexhaust, and in a second operative condition consistent with the pistonmoving in the opposite sense of axial direction closes communicationbetween said first control port and exhaust opens communication betweensaid second control port and exhaust.

The fluid pressure operated motor of the present invention in which thepiston is adapted to exhibit reciprocal movement can be of the typewhich is known in the art as a double acting device." To pro ide such adevice one pressure chamber can be alternately connected to fluidpressure and exhaust and the other pressure chamber simultaneously andalternately connected to exhaust and fluid pressure respectively. Toachieve this end the motor can include further valve means having afirst operative condition in which the second pressure chamber isadapted to communicate with fluid pressure and the first pressurechamber is adapted to communicate with exhaust by way of the firstcontrol port and a second operative condition in which the firstpressure chamber is adapted to communicate with fluid pressure and thesecond pressure chamber is adapted to communicate with exhaust by way ofthe second control port. The piston is caused to reciprocate in itscylinder by adjustment of the further valve means from its firstoperative condition to its second operative condition and vice versa. inthe double acting motor as above described the valve means and furthervalve means are preferably coupled together for simultaneous adjustmentfrom their respective first operative conditions to their respectivesecond operative conditions and vice versa; and conveniently the valvemeans and further valve means are incorporated in a spool valve in whichthe spool, at one end of its stroke, adjusts the spool valve to providethe above mentioned first operative conditions and the spool at theother end of its stroke adjusts the spool valve to provide theabove-mentioned second operative conditions.

It will be apparent that, in the double acting device, to obtaincontinuous reciprocation of the piston it is necessary for the valvemeans and further valve means to be adjusted alternately andsimultaneously between their first and second operative conditions.Preferably the valve means and further valve means are operativelycontrolled by the position of the piston in its cylinder so that withthe piston at or towards the end of its stroke in the one sense of axialdirection the valve means and further valve means are simultaneouslyadjusted from their first operative conditions to their second operativeconditions and with the piston at or towards the end of its stroke inthe opposite sense of axial direction the valve means and further valvemeans are simultaneously adjusted from their second operative conditionsto their first operative conditions. To achieve such an effect the spoolvalve can be fluid pressure operated so that the spool is reversed byalternately connecting one or more spool chambers in the spool valve tofluid pressure and exhaust, for example, as in a pressure biased spoolvalve or a double acting spool valve, and conveniently the communicationof fluid pressure and exhaust to the spool chamber or chambers iscontrolled by changeover valve means operatively coupled to the pistonso that at each end of stroke of the piston, the changeover valve meansreverses to reverse the spool from one end of its stroke to the other(and vice verse) to cause a reversal in the direction of movement of thepiston.

Although the motor of the present invention can provide a reciprocatingpiston with a nonadjustable, fixed length stroke,

in a further construction of the motor in accordance with the presentinvention in which a reciprocating piston and two pressure chambers areprovided, one or both ends of stroke of the piston can be axiallyadjustable relative to the piston cylinder so that the axial length ofstroke of the piston and/or the effective position about which thepiston reciprocates can be adjusted by predetermined axial distances. Ina construction of the motor in which the end of stroke of the piston inthe opposite sense of direction is determined, by the fixed location ofthe second control port, an axially disposed array of ports can beprovided in the piston cylinder and port selection means associatedtherewith by which at least one port in the array can be selected as thefirst control port for communication with exhaust and the end of strokeof the piston in the one sense of axial direction is determined when theselected port or ports of the array is closed by the piston land means.It may be desirable for both ends of stroke of the piston to be axiallyadjustable in which case a second axially disposed array of ports can beprovided in the piston cylinder and second port selection meansassociated therewith by which at least one port in the second array canbe selected as the second control port for communication with exhaustand the end of stroke of -the piston in the opposite sense of axialdirection is determined when the selected port or ports of the secondarray is closed by the piston land means.

Conveniently, particularly when the motor is to be applied in machinetool applications, only one of the two control ports need be capable ofbeing varied in an axial position. Such a construction is ofconsiderable value in machine tool applications since a cutting tool,for example a gear cutter, is often carried on the piston for reciprocalmovement and it is frequently desirable to have a fixed nonadjustableposition to which the cutter always moves at one end of stroke of thepiston and a predetermined but adjustable position to which the cutteralways moves at the other end of stroke of the piston.

In the motor in which provision is made for axial adjustment of oneadjustable both ends of stroke of the piston, it is neces sary for thetiming of the adjustment of the valve means and further valve means fromtheir first to their second operative conditions and vice versa to bemaintained in phase with the selected end or ends of stroke of thepiston and preferably reversal timing adjustment means is operativelyassociated with said valve means and further valve means whereby when anadjustment is made in the axial position of one or both ends of strokeof the piston an automatic adjustment is made to maintain the timing ofadjustment of the valve means and further valve means between theiroperative conditions in phase with the selected end or ends of stroke ofthe piston. When the end of stroke of the piston in the one sense ofaxial direction is axially adjustable, reversal timing adjustment meanscan be coupled for simultaneous adjustment with the port selection meansby which the first control port is selected. The arrangement of thereversal timing adjustment means is such that an adjustment in the axialposition at which the end of stroke of the piston is determined in theone sense of axial direction by the port selection means simultaneouslyeffects an adjustment of the timing at which the valve means and furthervalve means are adjusted from their first operative conditions to theirsecond operative conditions so that reversal of the valve means andfurther valve means remains in phase with the end of stroke of thepiston in the one sense of axial direction. Further, when the ends ofstroke of the piston in both senses of axial direction are axiallyadjustable, second reversal timing adjustment means can be operativelyassociated with the valve means and further valve means. The secondreversal timing adjustment means is coupled for simultaneous adjustmentwith the second port selection means and the arrangement of the secondreversal timing adjustment means is such that an adjustment in the axialposition at which the end of stroke of the piston is determined in theopposite sense of axial direction by the second port selection meanssimultaneously effects in an adjustment of the timing at which the valvemeans and further valve means are adjusted from their second operativeconditions to their first operative conditions so that reversal of thevalve means and further valve means remains in phase with the end ofstroke of the piston in the opposite sense ofaxial direction.

It will be apparent that the arrest of the piston at the end or ends ofits stroke can be very severe, particularly if the piston is, orcarries, a heavy load. If required a fluid resistance, as for example arestrictor, jet or the like, can be incorporated in the motor so thatthe or a pressure chamber when contracting is' adapted to communicatewith exhaust by way of the fluid resistance. By such an arrangement,when the control port through which the contracting pressure chamberexhausts is closed by the piston land means, the pressure chambermaintains communication with exhaust by way of the fluid resistance tocushion the end of stroke of the piston. In the construction of themotor having a reciprocating piston in which the pressure chambers areutilized to provide a double acting device it is preferred that eachpressure chamber, when contracting, communi ates with exhaust by way ofa fluid re sistance and the further valve means is arranged so that, inits first operative condition, it makes communication between the firstpressure chamber and exhaust by way of a fluid resistance and, initssecond operative condition, it makes communication between the secondpressure chamber and exhaust by way of a further fluid resistance,thereby cushioning both ends of stroke of the piston.

One embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying diagrammatic drawingsin which:

FIG. 1 shows an axial section through a hydraulic fluid pressureoperated motor constructed in accordance with the present invention inwhich reciprocation of the piston is controlled by a spool valve and theposition of the end of stroke of the piston in one axial direction canbe adjusted axially rela tive to the piston cylinder;

FIG. 2 illustrates a modification of the motor shown in FIG. I in whichthe positions of both ends of stroke of the piston are adjustableaxially relative to the piston cylinder;

FIG. 3 illustrates a further modification of the motor shown in FIG. 1in which the piston has a fixed length stroke and reversal of the spoolat the ends of stroke of the piston is controlled by valve meansincorporated in the piston and cylinder;

FIG. 4 illustrates a still further modification of the motor shown inFIG. 1 in which an end of stroke of the piston is adjustable axially andmeans is provided by which reversal of the spool is adapted to beeffected at the ends of stroke of the piston so that reversal of boththe spool and piston is maintained in phase; and

FIG. 5 illustrates a modification of the motor shown in FIG. 2 in whichboth ends of stroke of the piston are adjustable axially and means isprovided by which reversal of the spool is adapted to be effected at theends of stroke of the piston so that reversal of both the spool andpiston is maintained in phase.

Where possible throughout the following description, the same parts ormembers in each of the Figures have been accorded the same references.

The motor illustrated comprises a piston l which is slidably located formovement in an axial direction in a piston cylinder 2 defined by ahousing 3. The piston l extends, at each end, from the housing in sealedmanner and the piston cylinder 2 is provided with a stepped bore in thelarger diameter bore part 2a of which is slidably located a flange 4integrally formed with the piston. One side face of the flange 4 and theadjacent end part of the larger bore cylinder part 2a together define apressure chamber 5 and the other side face of the flange 4 and theadjacent end part of the larger bore cylinder part 20 together define afurther pressure chamber 6. It will be apparent that if the pressurechamber 5 is pressurized whilst the chamber 6 is exhausted the piston llwill move in an axial direction rightwardly in the drawing and if thechamber 6 is pressurized whilst the chamber 5 is exhausted the pistonwill move in an axial direction leftwardly in the drawing so that themechanism acts, in effect, as a double acting piston and cylinderdevice. The piston l is provided with an annular recess which defines anexhaust chamber 7 with the piston cylinder 2, the axial length of theexhaust chamber '7 being defined by a pair of axially spaced pistonlands ii and 9.

The motor further includes a spool valve shown generally at 10 in whicha stepped spool ll is slidably located for movement in an axialdirection in a spool cylinder l2 having a stepped bore which isconveniently defined by the housing 3. The spool 111 is located in itscylinder so that the smaller diameter of the spool is located in thesmaller bore of the spool cylinder and the larger diameter of the spoolis located in the larger bore of the spool cylinder. The smallerdiameter end T3 of the spool defines with one end part of the spoolcylinder 12 a constant pressure spool chamber lid and the largerdiameter end l5 of the spool defines with the other end part of thespool cylinder 12 an alternating pressure spool chamber lb. The spool isprovided with five lands T7 to 211 which define with the spool cylinderan array of axially spaced annular transfer chambers 22 to 25. Thetransfer chamber 22 is connected through a passage 26 in the housing 3to be in permanent communication with exhaust and the transfer chambers23 and 25 are each in permanent communication with exhaust throughhydraulic restrictors 27 and 2% respectively located in passages 29 and3b in the housing 3. The constant pressure spool chamber M is adapted tobe connected to a source of hydraulic fluid under constant pressure byway ofa passage Ell and the transfer chamber 24 communicates with theconstant pressure spool chamber M by way of an internal passage 32provided through the spool so that the transfer chamber 24l is alwaysunder pressure with the chamber lid. The alternating pressure spoolchamber lltS is adapted to be alternately connected, through passage 33and means shown generally at llltl, between a source of hydraulic fluidunder constant pressure and exhaust so that, with chamber Ml underpressure, when the chamber 16 is connected to exhaust the spool 11 movesaxially in the direction of its bias, i.e. rightwardly in the drawing,and when the alternately pressure chamber lb is connected to the sourceof hydraulic fluid under pressure the spool ll moves axially in thedirection against its bias, i.e. leftwardly in the drawing. it will beapparent that by alternating the chamber lo between fluid under pressureand exhaust the spool ill can be reciprocated intermittently orcontinuously.

The pressure chambers 5 and 6 communicate with the spool cylinder l2through passages 34 and 35 respectively and open into the spool cylinder12 through axially spaced ports 36 and 37 respectively. The ports 36 and37 are located so that at the end of the stroke of the spool ll in thedirection of its bias the port 36 communicates with transfer chambers 23and port 37 communicates with transfer chamber 2d (as illustrated). Theports 36 and 37 are respectively controlled by the lands l9 and 20 ofthe spool so that when the spool is moved to the opposite end of itsstroke in the direction against its bias the land 19 closes port 3b andreopens it to the transfer chamber 24 and simultaneously the land 20closes port 37 and reopens it to the transfer chamber 25. The transferchambers 23 and 25 are connected through passages 38 and 39 to be inpermanent communication with the piston cylinder 2. As illustrated, thepassage 39 is conveniently a branch of the passage 33. The passage 38opens into the piston cylinder 2 by way of an input port MB which islocated to be in permanent communication with the exhaust chamber 7.

Located in the piston cylinder 2 are control ports dll and 412 (see FIG.l) which are axially spaced from the port ll) and are axially disposedone on each side of the port dill. The control port $2 is controlled bythe piston land 9 during reciprocation of the piston so that it iseither closed by the land 9 or opens into the exhaust chamber 7.Similarly the control port ll is controlled by the piston land 8 duringreciprocation of the piston so that it is either closed by the land b oropens into the exhaust chamber 7.

The control port 42 communicates with the spool cylinder H by way of apassage l3 and opens into the spool cylinder through a port id. The port141 is located so that with the spool at the end of its stroke in thedirection of its bias, the port communicates with the transfer chamber22 (as illustrated). The port Ml is controlled by the spool land llll sothat as the spool moves towards and is located at the end of its strokein the direction against its bias the port 44 is closed by the land lid.The control port dll communicates through a passage 45 with a chamber 46in port selection means shown generally at d7. The chamber d6 is adaptedto be in permanent communication with a passage as which communicateswith the spool cylinder l2 ad opens into the spool cylinder by way of aport $9. The port M9 is located so that with the spool ill at the end ofits stroke in the direction against its bias the port opens into thetransfer chamber 22. The port 49 is controlled by the spool land 11! sothat when the spool is moved towards and is located at the end of itsstroke in the direction of its bias the port d9 is closed by the land 17(as illustrated). The ports 44 and T9 are axially spaced relative to theaxial spacing of the lands l7 and 11% so that both ports 4d and 49 donot simultaneously communicate with the transfer chamber 22.

The port selection means 437 conveniently comprises a cylindrical member50 which is capable of adjustable axial rotation within a sleeve fill.The member 50 is provided in its surface with a part annular recess 52which recess, together with the inner cylindrical wall of the sleeve 5l,defines the chamber as. A plurality (in this case four) of passages 45,4b, 53 and E l pass through the sleeve member to the cylinder member 50and communicate therewith in a peripherally spaced array so that byrotation of the cylinder member 50 the passage dd can communicate,through the chamber 46, solely with the passage 45, or with both thepassages d5 and 53, or with all the passages 45, 53, and 54. Alternativeconstructions for the port selection means 47 can be used, as forexample an adjustable spool valve.

The control ports 4111 and 42 are axially spaced relative to the pistonlands t3 and 9 so that when one control port is closed by its associatedland to communication with the exhaust chamber 7 the other control portis always in communication with the exhaust chamber 7. Further, assumingthat only one of the control ports ll and 41 2 communicates with theexhaust chamber 7, the control port which is open to chamber 7 is alsoadapted to communicate with exhaust by way of the transfer chamber 22and passage 26 by suitable positioning of the spool ill and the spool T1is adapted to control the flow of fluid under pressure and exhaust fromthe pressure chambers 5 and b so that the piston moves axially in adirection in which the control port which is open to the exhaust chamber7 is subsequently closed by its associated piston land whilst thatpiston land is moving in a direction towards the port 40.

We will now consider operation of the motor above described withreference to FIG. 1. A source of hydraulic fluid under constant pressureis connected to the passage 3T and the passages 26, 29, 3d and 33 areconnected to exhaust. The spool ll moves axially in the direction of itsbias until it abuts the housing 3 at the end of its stroke (asillustrated). Hydraulic fluid under pressure passes through the passage32, transfer chamber 241 and passage 35 into the pressure chamber 6. Thepressure chamber 5 is simultaneously connected to exhaust by way ofpassage 34, transfer chamber 23, passage 3%, exhaust chamber 7, controlport l2, passage 33, transfer chamber 22 and passage 2b. Consequentlythe piston l is moved axially in the direction of arrow X. The controlport M is effectively closed to exhaust since the port 49 in the spoolcylinder 12 is closed by the land l7. The piston ll continues to moveuntil the land 9 thereof closes the port 42 to communication with theexhaust chamber '7 which consequently shuts off communica tion betweenthe pressure chamber 5 and exhaust. A blockage is thereby formed to theexhaust of fluid from the pressure chamber 5 to arrest movement of thepiston l in the direction X irrespective of hydraulic fluid pressure inthe pressure chamber 6. it will be apparent that the arresting of thepiston can be severe and the arresting is conveniently cushioned by thehydraulic restrictor 27 which communicates with the transfer chamber 23.Hydraulic pressure builds up in the pres sure chamber when the controlport 42 closes and such pressure is fractionally relieved through therestrictor 27 to cushion the arrest of the piston.

For practical purposes, neglecting loss of fluid through the restrictor27, the end of stroke of the piston 1 subsequent to movement of thepiston in the direction X is the position at which the land 9 closes thecontrol port 42; the piston therefore remains at the end of its strokeuntil the pressure chambers S and 6 are connected to fluid underpressure and exhaust in a sense to move the piston axially in thedirection Y. This is achieved by axial movement of the spool 11 to theend of its stroke in the direction against its bias.

The passage 33 is connected to the source of hydraulic fluid underconstant pressure and hydraulic pressure in the alternating pressurespool chamber 16 moves the spool axially against its bias. In suchmovement of the spool the spool land 17 opens the port 49 to thetransfer chamber 22, the spool land 18 closes the port 44, the spoolland 19 closes the port 36 and reopens it to communication with thetransfer chamber 24 and the spool land 20 closes the port 37 and reopensit to communication with the transfer chamber 25. Hydraulic fluid underpressure can now pass from the transfer chamber 24 by way of port 36 andpassage 34 into the pressure chamber 5 whilst the pressure chamber 6communicates by way of passage 35, port 37, transfer chamber 25,passages 39 and 3t exhaust chamber '7, control port 41, passage 45,chamber 46, passage 48, port 49, transfer chamber 22 and passage 26 toexhaust. Consequently the piston l is caused to move axially in thedirection of arrow Y. The port 42 and passage 43 remain ineffectivesince the port 44 is closed to exhaust by the spool land 18.

The piston l continues to move in the direction of arrow Y until thepiston land 8 eventually shuts off communication between the controlport 41 and the exhaust chamber 7 which consequently shuts offcommunication between the pressure chamber 6 and exhaust and forms ablockage to the exhaust of fluid from the pressure chamber 6 to arrestthe piston irrespective of hydraulic fluid pressure in the pressurechamber 5. ln a similar manner to movement of the piston 1 in thedirection X, the arresting of movement of the piston is convenientlycushioned by the pressure chamber 6 communicating with exhaust throughthe hydraulic restrictor 28 and passage 30. For practical purposes,assuming negligible fluid loss through the restrictor 28, it will beapparent that the end of stroke of the piston l subsequent to itsmovement in the direction Y, corresponds to the position when thecontrol port 41 is shut off from communication to exhaust chamber 7 bythe piston land 8.

It is frequently desirable to adjust the axial length of stroke of thepiston 1 and this is conveniently achieved by providing means wherebythe position of the control port 41 can be selected from an axiallydisposed array of ports. ln the present example, the passages 53 and 54from the port selection means 47 communicate with the piston cylinder 2and open into the piston cylinder by way of ports 41a and Mbrespectively. The array of ports 41, 41a and 41b are located on the sideof the port 40 axially remote from the control port 42. Asaforementioned the end of stroke of the piston 1 subsequent to movementin the direction Y occurs when the port through which the exhaustchamber 7 communicates with exhaust is closed to exhaust by the pistonland 8. By rotating the cylinder member 50 in the direction or arrow Zthe exhaust chamber 7 can be further connected to exhaust by way of thepassages 45 and 53, or the passages 45, 53 and 54 as required. it willbe apparent that the shortest length of stroke of the piston 1 isobtained when the passages 53 and 54 are closed by the cylinder member50 and the longest stroke is obtained when the passages 48 and 54 are incommunication.

In the embodiment shown in FIG. 1 the axial length of stroke of theiston 1 is adjustable by provision of the array of ports 41, 41a, and41b and the port selection means 47. It will be apparent that theposition of the end of stroke in the direction Y of the piston relativeto the piston cylinder 2 can be adjusted axially by connecting thepassage 43 with one or more of the ports 41, 41a and 41b through theport selection means 47 whereas the position of the end of stroke in thedirection X of the piston relative to the piston cylinder is fixed andis determined by the piston land 9 closing control port 42. It may bedesirable to provide a motor in which the positions of both ends ofstroke of the piston are independently adjustable axially relative tothe piston cylinder and such a construction will now be considered withreference to FIG. 2 which illustratesa modification of the motor shownin FIG. 1.

in H6. 2 the axial position of the control port 42 (as referred to withreference to FIG. 1) is effectively selected from an axially disposedarray of ports all of which are located in the piston cylinder on theside of the port 40 axially remote from the array of ports 41, 41a and411). In the present example the control port 42 is effectively selectedfrom three ports 42a, 42b and 42c. he ports 42a, 42b and 42c communicateby way of passages 55 to 57 respectively with port selection means showngenerally at 58. The port selection means 58 is similarly constructed tothat shown at 47 and comprises a cylindrical member 59 which is capableof adjustable axial rotation within a sleeve 60. The member 59 isprovided in its surface with a part annular recess 61, which, togetherwith the inner cylindrical wall ofthe sleeve 60, defines a chamber 62.

The port 44 in the spool cylinder 12 communicates by way of passage 43awith the port selection means 58 to be in constant communication withthe chamber 62. The passages 55 to 57 pass through the sleeve member 60to the cylindrical member 59 and communicate therewith in a peripherallyspaced array so that by rotation of the member 59 the passage 43a cancommunicate, through the chamber 62 solely with the passage 55, or withboth passages 55 and 56, or with all the passages 55 to 57.

With the port se ection means 58 adjusted as shown in Fig. 2, passage43a communicates through chamber 62 solely with passage 55. Consequentlyas the piston 1 moves in the direction X, exhaust fluid from chamber 5flows by way of passage 34, transfer chamber 23, passage 38, exhaustchamber 7, port 42a, passage 55, chamber 62, passage 43a, transferchamber 22 and passage 26 to exhaust, and the end of stroke of thepiston in the direction X is determined when the selected and effectivecontrol port 43a is closed by piston land 9. It will be apparent that bysuitable adjustment of the member 59 the end of the stroke in thedirection X of the piston can be determined when the piston land 9closes the control port which can be port 42a or port 42!) or port 420.ln addition to providing adjustment in the positions of both ends ofstroke of the piston relative to the piston cylinder, the two arrays ofports 431, 41a, 41b and 42a, 42b, 42c and their respectively associatedport selection means 47 and 58 can be used to determine the length ofstroke of the piston and its effective center of reciprocation relativeto the piston cylinder. The shortest stroke of the piston 1 is obtainedwhen passage 418 communicates through chamber 46 with passage 45 andpassage 43a communicates through chamber 62 with passage 55 (as shown),and the longest stroke of the piston l is obtained when passage 48communicates through chamber 46 with passage 54 and passage 43acommunicates through chamber 62 with passage 57.

Conveniently the spool valve 10 is arranged so that it is caused toreverse automatically at the end of each stroke of the piston therebycausing the piston to reverse. This can be achieved by the alternatingpressure spool chamber 16 being connected alternately to exhaust andwith the source of fluid under constant pressure by way of valve meanswhich is controlled by reciprocation of the piston l and such aconstruction will now be described with reference to Fig. 3.

The motor shown in H6. 3 is similar to that shown in Fig. 1 with theexception that ports 41a, 41b and the port selection means 47 have beenomitted and control port 81 communicates through passage 45 directlywith port 49; consequently the piston 11 has a fixed length stroke andthe ends ofits strike, in the direction X, is determined by control port4-2 being closed by piston land 9 and, in the direction if by controlport ll-ll being closed by piston land 3.

The piston t has a further annular recess 63 which is formed betweenpiston lands 6d and 65. The recess 63 is located so that, at the end ofstroke of the piston in the direction X, it communicates with auxiliaryports 66 and 67 in the piston cylinder 2 and, at the end of stroke ofthe piston in the direction Y, it communicates with auxiliary ports 63and 69 in the piston cylinder. The auxiliary ports 66 and 63 communicateby way of passages 70, 7ll, 72 and 33 with the alternating pressurespool chamber 16, the port 67 is adapted to com municate by way ofpassage 73 with the source of fluid under pressure, and the port 69communicates by way of passage 74 with exhaust. The piston cylinder 2,piston lands 6d, 65 and auxiliary ports 66 to 69 effectively constitutea valve of the type which is known in the art as a changeover spoolvalve," the operation of which will now be described.

With the piston ll moving in the direction It, the end of stroke isdetermined by the control port 42 being closed by piston land 9 (asillustrated). The piston land 64 is arranged so that, immediately priorto control port l2 being closed, auxiliary port 66 is opened tocommunicate with recess 63 and therethrough with port 67 and fluidpressure. With passage 73 connected to the source of fluid pressure,fluid under pressure now passes by way of recess 63, port 66 andpassages 70, 72 and 33 to the alternating pressure spool chamber l6 (itbeing noted that port 63 is closed by the full diameter of the piston)thereby causing the spool ill to reverse and move in the directionagainst its bias. Reversal of the spool causes the piston to reverse andmove in the direction Y. With the piston moving in the direction Y, theend of stroke is determined by the control port ll being closed bypiston land The piston land 65 is arranged so that, immediately prior tocontrol port All being closed, auxiliary port 63 is opened tocommunicate with recess 63 and therethrough with port 69 and exhaust.The alternating pressure spool chamber 116 is now opened to ex haust byway of passages 33, 72, 7t, port 68, recess 63, port 69 and passage 74(it being noted that port 66 is closed by the full diameter of thepiston). The spool lll is thereby caused to reverse and move in thedirection of its bias and in so doing causes the piston l to reverse andmove in the direction X.

It will be realized that in constructions of the motor in which the endof stroke of the piston can be adjusted axially relative to the pistoncylinder either at one end of stroke as, for example, in theconstruction shown in FIG. 1, or at both ends of stroke as, for example,in the construction shown in FIG. 2, reversal timing adjustment meanscan be provided so that one or more auxiliary ports in the changeoverspool valve which determine the reversal of the spool lll can beselected from one or more arrays of auxiliary ports to ensure that thespool lll is caused to reverse at the end of the piston strokeirrespective of the relative position in the piston cylinder at whichthe piston stroke ends. To ensure that reversal of the spool llllremains in phase with reversal of the piston, said reversal timingadjustment means and the port selection means by which the control portor ports are selected are conveniently coupled together for simultaneousadjustment so that when the end or ends of stroke of the piston areadjusted the timing at which the spool llll is reversed issimultaneously adjusted to maintain reversal of the spool in phase withthe end or ends of stroke of the piston. A construction by whichreversal of the spool lll is maintained in phase with selected axialadjustment of one end of stroke of the piston T will now be consideredwith reference to FIG. Al.

The motor shown in FIG. 6 is similar to that shown in FIG. l in whichthe end of stroke of the piston l in the direction Y can be selectedfrom three positions and is achieved by adjustment of the port selectionmeans 47 to connect passage 4th with passage 45 or with passages 45 and53 or with passages 45, 53, and d.

Reversal timing adjustment means is incorporated in the port selectionmeans d7 and comprises a part annular recess 75 provided in thecylindrical member 50. The recess 75 is conveniently locateddiametrically opposite the recess 52. and, together with the innercylindrical wall of the sleeve 51, defines a chamber 76. Four passages77 to bl) pass through the sleeve member Eli to the cylinder member 50and communicate therewith in a peripherally spaced array so that byrotation of the cylinder member 50 the passage 77 can communicate,through chamber 76, solely with the passage 73, or only with bothpassages 78 and 76, or with all the passages 73 to till. The passage 77is located to be in constant communication with chamber 76 andcommunicates by way of the passage 72 with the alternating spool chamber116. The passages d6, d5, 53, 54 and 77 to tilt and chambers db and 76are so arranged in port selection means 47 that during rotation of themember fill, when passage 36 only communicates with passage d3, allpassages 73 to lid simultaneously communicate with passage 77; whenpassage till only communicates with passages 45 and 53, only passages 73and 79 communicates with passage 77; and when passage lib simultaneouslycommunicates with passages d5, .53 and 543, passage 77 only communicateswith passage 73.

The passages 73 to till communicate with auxiliary ports 63b, 63a and 66respectively in the piston cylinder 2. The ports 66b, 66a and 6b areaxially disposed in the piston cylinder in a similar array to the portsAll, Alllla and dllb respectively and are so controlled by piston land65 that during movement of the piston in the direction Y port 68 isfirst opened to recess 63 immediately before port All is closed bypiston land 3; thereafter port 63a is opened to recess 63 im mediatelybefore port lla is closed by piston land 3; and finally port 631; isopened to recess 63 immediately before port lllb is closed by pistonland 8. Ports 63, 63a and 63b, when opened by piston land 65 to recess63 communicate with exhaust by way of port 69 and passage 741.

In operation of the motor shown in Fig. 4 it will be apparent that theend of stroke of the piston in direction is determined by control portd2 being closed by piston land 9. lmmediately before control port 42 isclosed, auxiliary port 66 is opened by land 6d to recess 63 and therebyto fluid pressure through port 67. The alternating pressure spoolchamber 16 is pressurized and the spool reverses thereby reversing thepiston l. With the cylindrical member Ell adjusted to the positionillustrated in PM]. 4-, as the piston moves in the direction Y, fluidfrom pressure chamber 6 passes to exhaust solely by way of port ill and,immediately before port ll is closed by piston land 6, auxiliary port 66is opened to exhaust by way of recess 63 and port 6'3. Consequently thealte'mating pressure spool chamber 16 is opened to exhaust by way ofpassages 33, 72 and 77, chamber 76 and passage till thereby causing thespool to reverse and move in the direction of its bias to reverse thepiston so that it again moves in the direction X.

If the cylindrical member Ell is adjusted by rotation in the direction 2so that passage did only communicates with both passages d5 and 53, theend of stroke of' the piston in direction Y is determined when pistonland 33 closes port Ma; however, by said adjustment of the member Ell,passage 77 only communicates through chamber 76 with passages 73 and 79.Consequently during movement of the piston in direction Y the pistonland 65 opens auxiliary port 68 without effect and the alternatingpressure spool chamber is exhausted only when the piston land 63 opensport 63a to-port 69 by way of recess 63 which takes place immediatelybefore port dlla is closed.

If the cylindrical member 5% is further adjusted in direction Z so thatPASSAGE d3 communicates with passages 45, 53 and 5d, the end of strokeof the piston in direction Y is determined when piston land 3 closesport lib; however by saidfurther adjustment of the member 50, passage 77only communicates through chamber 76 with passage 73. Consequentlyduring movement of the piston in the direction Y, the piston land 65opens auxiliary ports 63 and 68a without effect and the alternatingpressure spool chamber 116 is exhausted only iii when piston land 65opens auxiliary port 6817 to port 69 by way of recess 63 which takesplace immediately before port 8112 is closed.

In FIG. 4 the end of stroke of the piston l in the direction X isdetermined by control port 42 being closed by piston land 9 and the endof stroke of the piston in the direction Y is axially adjustable to oneof three positions by adjustment of the port selection means 47 and, asabove described, the reversal of the spool 11 to reverse the piston isautomatically maintained in phase with the selected end of stroke of thepiston in the direction Y by alteration of the reversal timingadjustment means incorporated in the port selection means 47 to controlcommunication between the alternating pressure spool chamber 16 andexhaust by way of the array of auxiliary ports 68, 68a and 68b. In themotor shown in FIG. 2 the end of stroke of the piston 1 in the directionX is axially adjustable to one of three positions by adjustment of theport selection means 58 and the end of stroke of the piston in thedirection Y is axially adjustable to one of three positions byadjustment of the port selection means 47 and a construction will now bedescribed with reference to Fig. by which the reversal of the spool 11to reverse the piston is automatically maintained in phase with theselected ends of stroke of the piston in both axial directions.

As will be apparent from an understanding of the motor shown in FIG. 4,the end of stroke in the direction Y of the piston 1 in FIG. 5 isaxially adjustable to one of three positions by adjustment of the portselection means 47 and reversal of the spool 11 to reverse the piston isautomatically maintained in phase with the selected end of stroke of thepiston in the direction Y in an identical manner to that above describedwith reference to FIG. 4. Referring to FIG. 5, the port selection means58 incorporates reversal timing adjustment means which includes a partannular recess 8i provided in the cylindrical member 59. The recess 81is conveniently located diametrically opposite the recess 61 and,together with the inner cylindrical wall of the sleeve 60, defines achamber 82. Four passages 83 to 85 and 79a pass through the sleevemember 60 and communicate therewith in a peripherally spaced array sothat by rotation of the cylinder member 59 the passage 70a cancommunicate, through chamber 82, with all passages 83 to $5 or only withboth passages 84% and 85 solely with passage 35. The passage 70a islocated to be in constant communication with chamber 82 and communicatesby way of passage 72 with the alternating pressure spool chamber 16. Thepassages 43a, 55 to 57, 70a and 83 to 85 and chambers 62 and 82 are soarranged in the port selection means 58 that during rotation of thecylinder member 59, when passage 430 only communicates with passage 55,all passages 83 to 85 simultaneously communicate with passage 70a; whenpassage 43a only communicates with passages 55 and 56, passage 70a onlycommunicates with passages 84 and 85; and when passage 43a communicateswith all passages 55 to 57, passage 70a only com municates with passage85.

The passages 83 to 85 communicate with auxiliary ports 66a, 66b and 66crespectively in the piston cylinder 2. The ports 66a, 66b, and 660 areaxially disposed in the piston cylinder 2 in a similar array to theports 42a, 42b and 420 respectively and are so controlled by piston land64 that during movement of the piston in the direction X port 66a isfirst opened to recess 63 immediately before port 4120 is closed bypiston land 9; thereafter port 66b is opened to recess 63 immediatelybefore port 42b is closed by piston land 9; and finally port 66c isopened to recess 63 immediately before port 42c is closed by piston land9. Ports 66a, 66b and 660, when opened by piston land 64 to recess 63,communicate with port 67 which is adapted to be connected to a source offluid pressure by way ofpassage 73.

In operation of the motor shown in FIG. 5 it will be apparent that theselected end of stroke of the piston I in the direction Y and phasedreversal of the spool at said selected end of stroke of the piston isachieved in an identical manner to that in the motor described withreference to FIG. 4. At the end of stroke of the piston in the directionY the spool is automatically reversed by exhausting of the alternatingpressure spool chamber 16 and the spool valve 10 is adjusted to thecondition shown in FIG. 5 thereby causing the piston l to reverse andmove in the direction X.

With the cylindrical member 59 adjusted to the position shown in FIG. 5and the piston moving in the direction X, fluid from pressure chamber 5passes to exhaust solely by way of port 420 and, immediately before port42a is closed by piston land 9, auxiliary port 660 is opened to fluidpressure by way of recess 63 and port 67. Consequently the alternatingpressure spool chamber communicates with fluid pressure by way ofpassages 33, 72, a chamber 82 and passage 83 thereby causing the spoolto reverse and move in the direction against its bias to reverse thepiston so that it again moves in the direction Y.

If the cylindrical member 59 is adjusted by rotation in the direction Zso that passage 43a only communicates through chamber 62 with bothpassages 55 and 56, the end of stroke of the piston in the direction Xis determined when the piston land 9 closes port 42b; however, by saidadjustment of the member 59, passage 70a only communicates throughchamber 82 with passages 84 and 85. Consequently during movement of thepiston in direction X the piston land 64 opens auxiliary port 66awithout effect and the alternating pressure spool chamber 16communicates with fluid pressure only when land 64 opens port 66b toport 67 by way of recess 63 which takes place immediately before port4212 is closed.

If the cylindrical member 59 is further adjusted in the direction Z sothat passage 430 communicates with passages 55 to 57, the end of strokeof the piston in the direction X is determined when the piston land 9closes port 420; however by said further adjustment of the member 59,passage 70a only communicates by way of chamber 82 with passage 85.Consequently during movement of the piston in the direction X the pistonland 64 opens auxiliary ports 66a and 66b without effect and thealternating pressure spool chamber 16 communicates with fluid pressureonly when land 64 opens port 66c to port 67 by way of recess 63 whichtakes place immediately before port 42c is closed.

Iclaim:

I. A fluid pressure operated motor, comprising in combination:

a. a piston slidably mounted in a piston cylinder;

b. means to permit axial movement of said piston; including:

1. means to exhaust fluid from a first pressure chamber associatedtherewith;

c. means to arrest said piston at the end of its stroke in one sense ofaxial direction, including:

1. means communicating said first pressure chamber with a first controlport in said piston cylinder;

2. means to exhaust fluid from said first pressure chamber through saidfirst control port;

3. and first piston land means controlling said fluid ex haust throughsaid first control port by closing said first control port to form ablockage to said fluid exhaust to arrest said piston at said one end ofstroke;

d. means to alternately contract and expand a second pres sure chamberconcurrently with alternate expansion and contraction of said firstpressure chamber during reciprocation of said piston;

e. means to arrest said piston at the end of its stroke in a secondsense of axial direction, including:

1. means communicating said second pressure chamber with a secondcontrol port;

2. means to exhaust fluid from said second pressure chamber through saidsecond control port;

3. and second piston land means controlling said fluid exhaust throughsaid second control port by closing said second control port to form ablockage to said fluid exhaust to arrest said piston at said second endof stroke;

f. said first and second piston land means, together with said pistoncylinder, defining an exhaust chamber communicating with each saidpressure chamber in its contracting phase;

g. and means to maintain at least one ofsaid first and second controlports in communication with said exhaust chamber, including:

1. valve means closing communication between said second control portand exhaust and opening communication between said first control portand exhaust, in a first operative position;

2. said valve means opening communication between said second controlport and exhaust and closing communication between said first controlport and exhaust, in a second operative position.

2. A fluid pressure operated motor as defined in claim ll, furthercomprising:

a. further valve means having a first operative condition wherein saidsecond pressure chamber communicates with a fluid under pressure andsaid first pressure chamber communicates with exhaust through said firstcontrol port;

b. said further valve means having a second operative condition whereinsaid first pressure chamber communicates with a fluid under pressure andsaid second pressure chamber communicates with exhaust through saidsecond control port;

c. and means to adjust said further valve means from said firstoperative condition to said second operative condition and vice versa tothereby reciprocate said piston.

3. A fluid pressure operated motor as defined in claim 2 furthercomprising:

a. at least one input port in said piston cylinder axially disposedbetween said first and second control ports, said input port being incommunication with said exhaust chamber during reciprocation of saidpiston;

b. said further valve means communicating said first and second pressurechambers with said input port;

c. said first piston land means closing said first control port tocommunication with said exhaust chamber during movement of said firstpiston land means axially toward said input port;

d. said second piston land means closing said second control port tocommunication with said exhaust chamber during movement of said secondpiston land means axially toward said input port.

t. A fluid pressure operated motor as defined in claim 2, furthercomprising means to couple said valve means and said further valve meanstogether for substantially simultaneous adjustment from their respectivefirst operative conditions to their respective second operativeconditions and vice versa.

5. A fluid pressure operated motor as claimed in claim 4, wherein saidvalve means and said further valve means are provided by a spool valvewhich comprises a spool axially slidable for reciprocation in a spoolcylinder wherein said spool, at one end of its stroke, has means toadjust said spool valve to provide said first operative conditions and,at the other end to its stroke, has means to adjust said spool valve toprovide said second operative conditions.

6. A fluid pressure operated motor as claimed in claim 5, wherein thespool valve is pressure biased and the spool has opposed working facesof different effective areas, the working face of smaller effective areadefining with one part of the spool cylinder at constant pressure spoolchamber connected to a source of fluid under constant pressure and theworking face of larger effective area defining with another part of thespool cylinder an alternating pressure spool chamber and having means tocommunicate alternately with fluid under pres sure and with exhaust toreciprocate said spool when the constant pressure spool chambercommunicates with fluid pres sure.

7. A fluid pressure operated motor as claimed in claim 6, wherein saidvalve means and said further valve means are lid operatively controlledby the position of the piston in its cylinder wherein, with said pistonadjacent the end of its stroke in said one sense of axial direction saidvalve means and further valve means are substantially simultaneouslyadjusted from said first operative conditions to said second operativeconditions and with the piston adjacent the end ofits stroke in saidsecond sense of axial direction said valve means and further valve meansare simultaneously adjusted from said second operative conditions tosaid first operative conditions.

d. A fluid pressure operated motor as claimed in claim 7, furthercomprising changeover valve: means to control the flow of fluid underpressure to, and exhaust from, said alternating pressure spool chamber,said changeover valve means being operatively coupled to said piston;wherein, in a first operative condition, at one end of stroke of thepiston, said alternating pressure spool chamber is connected by saidchangeover valve means to exhaust to move said spool to the end of itsstroke in the direction of its bias, and in a second operativecondition, at the other end of stroke of said piston, said alternatingpressure spool chamber is connected by said changeover valve means tofluid under pressure to reverse said spool and move it axially to theend of stroke in the direction against its bias.

9. A fluid pressure operated motor as claimed in claim 8, wherein saidchangeover valve means comprises auxiliary ports in said pistoncylinder; and further piston land means controlling the communication ofsaid. auxiliary ports to fluid under pressure and exhaust duringreciprocation of said piston.

Jill. A fluid pressure operated motor as claimed in claim ll, furthercomprising an array of ports axially diaposed in said piston cylinderand port selection means to select at least one port in said array asthe first control port for communication with exhaust, the end of strokeof the piston in said one sense of axial direction being determined whensaid selected at least one port is closed by said piston land means.

ill. A fluid pressure operated motor as claimed in claim I, furthercomprising:

a. a first array of ports axially disposed in said piston cylinder andfirst port selection means to select at least one port in said firstarray as the first control port, the end of stroke of said piston insaid one sense of axial direction being determined when the selected atleast one port of said first array is closed by said piston land means;

b. and a second array of ports axially disposed in said piston cylinderand second port selection means to select at least one port in saidsecond array as the second control port for communication with exhaust,the end of stroke of said piston in said second sense of axial directionbeing deter mined when the selected at least one port of said secondarray is closed by said piston land means.

112. A fluid pressure operated motor as defined in claim 7,

further comprising:

a. an array of ports axially disposed in said piston cylinder;

b. port selection means to select at least one port in said array as thefirst control port for communication with ex haust, the end of stroke ofsaid piston in said one sense of axial direction being determined whensaid selected at least one port is closed by said piston land means;

c. reversal timing adjustment means operatively associated with saidvalve means and said further valve means, said reversal timingadjustment means being coupled for sub stantially simultaneousadjustment with said port selection means.

113. A fluid pressure operated motor as defined-in claim 7 furthercomprising:

a. a first array of ports axially disposed in said piston cylinder;

b. first port selection'means to select at least one port in said firstarray as the first control port, the end of stroke of. said piston insaid one sense of axial direction being determined when the selected atleast one port of said first array is closed by said piston land means;

0. a second array of ports axially disposed in said piston from, saidalternating pressure spool chamber, said chancylinder; geover valvemeans being operatively coupled to said d. second port selection meansto select at least one port in piston;

said second array as the second control port for commufurther pistonland means controlling the communication nication with exhaust, the endof stroke of said piston in of said auxiliary ports to fluid underpressure and exhaust said second sense of axial direction beingdetermined during reciprocation of said piston;

when the selected at least one ort of aid cond arr i 0. wherein saidreversal timing adjustment means comprises closed by said piston landmeans; an array of auxiliary ports axially disposed in said piston e.first reversal timing adjustment means operatively ascylinder andcontrolled by said further piston land means; sociated with id lv meansd id f h valve d. auxiliarv ports selection means to select at least oneauxmeans, said first reversal timing adjustment means being iliary p tin sald y. Said xili ry p r lecti n coupled for substantiallysimultaneous adjustment with means fg Coupled for suPstamlanySlmultaneous said first rt el ti m justment with said port selectionmeans;

f. and second reversal timing adjustment means operatively and S3id a|t?matif1g P spool P alternately associated with said valve means and saidfurther valve commumcalmg Wm] exhaust and lq under P means, Said Secondreversal timing adjustment means sure through said selected at least oneauxiliary port at a being coupled for substantially simultaneousadjustment predetqmmed end of Stroke ofsald P with Said second portSelection means 15. A fluid pressure operated motor as defined in claim1,

4 A fluid pressure Opel-med motor as defined in claim 12, furthercomprising, fluid resistance means and means to comfunher comprising;municate each contracting pressure chamber with exhaust a. changeovervalve means comprising auxiliary ports in through "P reslstancc means tocushlo the end of said piston cylinder, said changeover valve means con-Stroke ofsa'd trolling the flow of fluid under pressure to, and exhaust

1. A fluid pressure operated motor, comprising in combination: a. apiston slidably mounted in a piston cylinder; b. means to permit axialmovement of said piston; including:
 1. means to exhaust fluid from afirst pressure chamber associated therewith; c. means to arrest saidpiston at the end of its stroke in one sense of axial direction,including:
 1. means communicating said first pressure chamber with afirst control port in said piston cylinder;
 2. means to exhaust fluidfrom said first pressure chamber through said first control port;
 3. andfirst piston land means controlling said fluid exhaust through saidfirst control port by closing said first control port to form a blockageto said fluid exhaust to arrest said piston at said one end of stroke;d. means to alternately contract and expand a second pressure chamberconcurrently with alternate expansion and contraction of said firstpressure chamber during reciprocation of said piston; e. means to arrestsaid piston at the end of its stroke in a second sense of axialdirection, including:
 1. means communicating said second pressurechamber with a second control port;
 2. means to exhaust fluid from saidsecond pressure chamber through said second control port;
 3. and secondpiston land means controlling said fluid exhaust through said secondcontrol port by closing said second control port to form a blockage tosaid fluid exhaust to arrest said piston at said second end of stroke;f. said first and second piston land means, together with said pistoncylinder, defining an exhaust chamber communicating with each saidpressure chamber in its contracting phase; g. and means to maintain atleast one of said first and second control ports in communication withsaid exhaust chamber, including:
 1. valve means closing communicationbetween said second control port and exhaust and opening communicationbetween said first control port and exhaust, in a first operativeposition;
 2. said valve means opening communication between said secondcontrol port and exhaust and closing communication between said firstcontrol port and exhaust, in a second operative position.
 2. means toexhaust fluid from said first pressure chamber through said firstcontrol port;
 2. means to exhaust fluid from said second pressurechamber through said second control port;
 2. said valve means openingcommunication between said second control port and exhaust and closingcommunication between said first control port and exhaust, in a secondoperative position.
 2. A fluid pressure operated motor as defined inclaim 1, further comprising: a. further valve means having a firstoperative condition wherein said second pressure chamber communicateswith a fluid under pressure and said first pressure chamber communicateswith exhaust through said first control port; b. said further valvemeans having a second operative condition wherein said first pressurechamber communicates with a fluid under pressure and said secondpressure chamber communicates with exhaust through said second controlport; c. and means to adjust said further valve means from said firstoperative condition to said second operative condition and vice versa tothereby reciprocate said piston.
 3. and second piston land meanscontrolling said fluid exhaust through said second control port byclosing said second control port to form a blockage to said fluidexhaust to arrest said piston at said second end of stroke; f. saidfirst and second piston land means, together with said piston cylinder,defining an exhaust chamber communicating with each said pressurechamber in its contracting phase; g. and means to maintain at least oneof said first and second control ports in communication with saidexhaust chamber, including:
 3. and first piston land means controllingsaid fluid exhaust through said first control port by closing said firstcontrol port to form a blockage to said fluid exhaust to arrest saidpiston at said one end of stroke; d. means to alternately contract andexpand a second pressure chamber concurrently with alternate expansionand contraction of said first pressure chamber during reciprocation ofsaid piston; e. means to arrest said piston at the end of its stroke ina second sense of axial direction, including:
 3. A fluid pressureoperated motor as defined in claim 2, further comprising: a. at leastone input port in said piston cylinder axially disposed between saidfirst and second control ports, said input port being in communicationwith said exhaust chamber during reciprocation of said piston; b. saidfurther valve means communicating said first and second pressurechambers with said input port; c. said first piston land means closingsaid first control port to communication with said exhaust chamberduring movement of said first piston land means axially toward saidinput port; d. said second piston land means closing said second controlport to communication with said exhaust chamber during movement of saidsecond piston land means axially toward said input port.
 4. A fluidpressure operated motor as defined in claim 2, further comprising meansto couple said valve means and said further valve means together forsubstantially simultaneous adjustment from their respective firstoperative conditions to their respective second operative conditions andvice versa.
 5. A fluid pressure operated motor as claimed in claim 4,wherein said valve means and said further valve means are provided by aspool valve which comprises a spool axially slidable for reciprocationin a spool cylinder wherein said spool, at one end of its stroke, hasmeans to adjust said spool valve to provide said first operativeconditions and, at the other end to its stroke, has means to adjust saidspool valve to provide said second operative conditions.
 6. A fluidpressure operated motor as claimed in claim 5, wherein the spool valveis pressure biased and the spool has opposed working faces of differenteffective areas, the working face of smaller effective area definingwith one part of the spool cylinder a constant pressure spool chamberconnected to a source of fluid under constant pressure and the workingface of larger effective area defining with another part of the spoolcylinder an alternating pressure spool chamber and having means tocommunicate alternately with fluid under pressure and with exhaust toreciprocate said spool when the constant pressure spool chambercommunicates with fluid pressure.
 7. A fluid pressure operated motor asclaimed in claim 6, wherein said valve means and said further valvemeans are operatively controlled by the position of the piston in itscylinder wherein, with said piston adjacent the end of its stroke insaid one sense of axial direction said valve means and further valvemeans are substantially simultaneously adjusted from said firstoperative conditions to said second operative conditions and with thepiston adjacent the end of its stroke in said second sense of axialdirection said valve means and further valve means are simultaneouslyadjusted from said second operative conditions to said first operativeconditions.
 8. A fluid pressure operated motor as claimed in claim 7,further comprising changeover valve means to control the flow of fluidunder pressure to, and exhaust from, said alternating pressure spoolchamber, said changeover valve means being operatively coupled to saidpiston; wherein, in a first operative condition, at one end of stroke ofthe piston, said alternating pressure spool chamber is connected by saidchangeover valve means to exhaust to move said spool to the end of itsstroke in the direction of its bias, and in a second operativecondition, at the other end of stroke of said piston, said alternatingpressure spool chamber is connected by said changeover valve means tofluid under pressure to reverse said spool and move it axially to theend of stroke in the direction against its bias.
 9. A fluid pressureoperated motor as claimed in claim 8, wherein said changeover valvemeans comprises auxiliary ports in said piston cylinder; and furtherpiston land means controlling the communication of said auxiliary portsto fluid under pressure and exhaust during reciprocation of said piston.10. A fluid pressure operated motor as claimed in claim 1, furthercomprising an array of ports axially diaposed in said piston cylinderand port selection means to select at least one port in said array asthe first control port for communication with exhaust, the end of strokeof the piston in said one sense of axial direction being determined whensaid selected at least one port is closed by said piston land means. 11.A fluid pressure operated motor as claimed in claim 1, furthercomprising: a. a first array of ports axially disposed in said pistoncylinder and first port selection means to select at least one port insaid first array as the first control port, the end of stroke of saidpiston in said one sense of axial direction being determined when theselected at least one port of said first array is closed by said pistonland means; b. and a second array of ports axially disposed in saidpiston cylinder and second port selection means to select at least oneport in said second array as the second control port for communicationwith exhaust, the end of stroke of said piston in said second sense ofaxial direction being determined when the selected at least one port ofsaid second array is closed by said piston land means.
 12. A fluidpressure operated motor as defined in claim 7, further comprising: a. anarray of ports axially disposed in said piston cylinder; b. portselection means to select at least one port in said array as the firstcontrol port for communication with exhaust, the end of stroke of saidpiston in said one sense of axial direction being determined when saidselected at least one port is closed by said piston land means; c.reversal timing adjustment means operatively associated with said valvemeans and said further valve means, said Reversal timing adjustmentmeans being coupled for substantially simultaneous adjustment with saidport selection means.
 13. A fluid pressure operated motor as defined inclaim 7, further comprising: a. a first array of ports axially disposedin said piston cylinder; b. first port selection means to select atleast one port in said first array as the first control port, the end ofstroke of said piston in said one sense of axial direction beingdetermined when the selected at least one port of said first array isclosed by said piston land means; c. a second array of ports axiallydisposed in said piston cylinder; d. second port selection means toselect at least one port in said second array as the second control portfor communication with exhaust, the end of stroke of said piston in saidsecond sense of axial direction being determined when the selected atleast one port of said second array is closed by said piston land means;e. first reversal timing adjustment means operatively associated withsaid valve means and said further valve means, said first reversaltiming adjustment means being coupled for substantially simultaneousadjustment with said first port selection means; f. and second reversaltiming adjustment means operatively associated with said valve means andsaid further valve means, said second reversal timing adjustment meansbeing coupled for substantially simultaneous adjustment with said secondport selection means.
 14. A fluid pressure operated motor as defined inclaim 12, further comprising: a. changeover valve means comprisingauxiliary ports in said piston cylinder, said changeover valve meanscontrolling the flow of fluid under pressure to, and exhaust from, saidalternating pressure spool chamber, said changeover valve means beingoperatively coupled to said piston; b. further piston land meanscontrolling the communication of said auxiliary ports to fluid underpressure and exhaust during reciprocation of said piston; c. whereinsaid reversal timing adjustment means comprises an array of auxiliaryports axially disposed in said piston cylinder and controlled by saidfurther piston land means; d. auxiliary ports selection means to selectat least one auxiliary port in said array, said auxiliary port selectionmeans being coupled for substantially simultaneous adjustment with saidport selection means; e. and said alternating pressure spool chamberalternately communicating with exhaust and with fluid under pressurethrough said selected at least one auxiliary port at a predetermined endof stroke of said piston.
 15. A fluid pressure operated motor as definedin claim 1, further comprising, fluid resistance means and means tocommunicate each contracting pressure chamber with exhaust through saidfluid resistance means to cushion the end of stroke of said piston.